1. Field of the Invention
The present invention relates to an air-conditioning apparatus of a vehicle. More particularly, the present invention relates to a temperature control means installed inside a vehicle for use in the event of a failure of a sensor provided in the vehicle.
2. Description of the Related Art
As is commonly known, an air-conditioning duct of a vehicle is equipped with a blower, an evaporator, a heater, air-mix flaps and outlet flaps. The blower takes in external air, introducing it to the inside of the vehicle as well as circulates air inside the vehicle. The evaporator reduces the temperature and the humidity of the air blown by the blower. The heater heats the air blown by the blower. The air-mix flaps regulate the amount of air blown to the heater. The outlet flaps distribute air adjusted to a predetermined temperature to appropriates outlets. Thus, air which has been cooled and dehumidified by the evaporator, or air heated by the heater after being cooled and dehumidified by the evaporator is distributed to the outlets in the vehicle.
The air-flow quantity of the blower, the opening of the air-mix flap and switching positions of the outlet flaps are controlled by commands issued by a control unit. To put it in detail, the control unit computes the temperature of air blown from the outlets (outlet temperature) from an internal air temperature (set temperature) set by the user as well as an external temperature, an engine water temperature, a sun load, a vehicle speed and the air-flow quantity, which are measured by sensors. Then, the control unit computes control signals for the blower, the air-mix flaps and the outlet flaps by using the outlet temperature as a parameter. Subsequently, the control unit supplies the control signals to motors for driving the blower, the air-mix flaps and the outlet flaps in order to adjust the air-flow quantity of the blower, the opening of the air-mix flaps and the switching positions of the outlet flaps.
By the way, in the event of a failure occurring in a sensor such as an internal-air-temperature sensor and an external air temperature sensor required in the computation of the outlet temperature in the air-conditioning apparatus having the configuration described above, the outlet temperature cannot be calculated. When a failure occurs in such a sensor, it is thus impossible to control the air-flow quantity of the blower, the opening of the air-mix flaps and switching positions of the outlet flaps.
Thus, in order to solve the problem described above, the control unit employed in the conventional air-conditioning apparatus is monitoring the operations of the sensors in order to determine whether or not the sensors operate normally. In the event of a failure occurring in a sensor, the control unit uses a value serving as a substitute for a value supposed to be output by the failing sensor in the computation of an outlet temperature to be used later in control of the air-flow quantity of the blower, the opening of the air-mix flaps, and the switching positions of the outlet flaps. The substitute value is registered in advance.
In the event of a failure occurring in a sensor, since computation of the outlet temperature, control of air-flow quantity of the blower, control of the opening of the air-mix flap and control of switching position of the outlet flaps are carried out using a constant substitute value regardless of the actual value, leaving the case of the substitute value close to an actual sensor value out of the question, there is raised a problem of impossibility to properly execute control based on a reality in case a substitute value is much different from an actual sensor value. In particular, the opening of the air-mix flaps is directly related to the temperature of air blown to the inside of the vehicle from the outlet. Thus, unless control of the opening of the air-mix flaps is executed on the basis of a reality, the temperature of air actually blown to the inside of the vehicle from the outlets is greatly different from the air temperature desired by a passenger, raising a problem of discomfort felt by the passenger.
It is thus an object of the present invention to provide a vehicle""s air-conditioning apparatus capable of supplying air at a temperature desired by a passenger from outlets even in the event of a failure occurring in a sensor.
In order to solve the problem described above the present invention comprises: a blower, an evaporator, a heater, air-mix flaps and outlet flaps, which are provided in an air conditioning duct of the vehicle; sensors for detecting input parameters required in computation of an outlet temperature; and a control unit for inputting signals generated by the sensors as well as controlling an air-flow quantity of the blower and controlling an opening of the flaps, wherein the control unit monitors the sensors to determine whether the sensors are functioning normally and, when one or some of the sensors are determined to have failed, the control unit computes the outlet temperature using the replacement value registered in advance each serving as a substitute for a value supposed to be outputted by one of the failing sensors, switches positions of the outlet by controlling the air-flow quantity of the blower and opening of the outlet flaps based on the computed value, and controls the opening of the air-mix flaps based on a set value set by the user independently of the outlet temperature computed by using the replacement values.
As described above, a passenger is allowed at least to set the temperature of air blown from the outlets at a desired value in case the replacement value is greatly different from the actual air temperature. Thus, it is possible to solve or lessen the problem of discomfort felt by the passenger due to excessively cold or excessively hot blown air.
The opening of the air-mix flap can be subjected to uniformly proportional control according to the set temperature or multi-stage proportional control according to the set temperature. Appropriate temperature adjustment can be carried out by subjecting the opening of the air-mix flap to a uniformly proportional control. Further, since a control in response to a capacity of the heater provided to a duct system can be realized by subjecting the opening of the air-mix flap to a multi-stage proportional control, fine temperature adjustment is possible.